6533b872fe1ef96bd12d421f

RESEARCH PRODUCT

A family of enneanuclear iron(II) single-molecule magnets.

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Complexes [Fe 9 (X) 2 -(02CMe)8{(2-py) 2 CO 2 } 4 ] (X - = OH (1), N 3 - (2), and NCO- (3)) have been prepared by a route previously employed for the synthesis of analogous Co 9 and Ni 9 complexes, involving hydroxide substitution by pseudohalides (N 3 - , NCO-). As indicated by DC magnetic susceptibility measurements, this substitution induced higher ferromagnetic couplings in complexes 2 and 3, leading to higher ground spin states compared to that of 1. Variable-field experiments have shown that the ground state is not well isolated from excited states, as a result of which it cannot be unambiguously determined. AC susceptometry has revealed out-of-phase signals, which suggests that these complexes exhibit a slow relaxation of magnetization that follows Arrhenius behavior, as observed in single-mole-cule magnets, with energy barriers of 41 K for 2 (τ 0 =3.4×10 -12 s) and 44K for 3 (τ 0 =2.0×10 -11 s). Slow magnetic relaxation has also been observed by zero-field 57 Fe Mossbauer spectroscopy. Characteristic integer-spin electron paramagnetic resonance (EPR) signals have been observed at X-band for 1, whereas 2 and 3 were found to be EPR-silent at this frequency. 1 H NMR spectrometry in CD 3 CN has shown that complexes 1-3 are stable in solution.